1. Field of the Invention
The present invention relates to a formed zeolite honeycomb article and a fired zeolite honeycomb article. More particularly, it relates to a formed zeolite honeycomb article in which generation of cracks due to a drying shrinkage is effectively suppressed during drying, and a fired zeolite honeycomb article having an excellent mechanical strength.
2. Description of the Related Art
It is known that zeolite is a type of silicate having a mesh crystal structure provided with fine pores having a uniform diameter, there are present various chemical compositions represented by the general formula: WmZnO2n.sH2O (W: sodium, potassium, calcium or the like, Z: silicon, aluminum or the like, and s takes various values), and there are present many kinds (types) of crystal structures having different pore shapes. Zeolite has an inherent adsorption ability, catalyst performance, solid acid characteristics, ion exchange ability and the like based on the respective chemical compositions or crystal structures, and is utilized in various use applications such as an adsorbing material, a catalyst, a catalyst carrier, a gas separation membrane and an ion exchanger (e.g., see Patent Documents 1 to 3).
For example, MFI-type zeolite (also referred to as “ZSM-5 type zeolite”) is provided with pores each having a size of about 0.5 nm by oxygen ten-membered rings among crystals, and is utilized in a use application such as an adsorbing material for adsorbing nitrogen oxides (NOx), hydrocarbons (HC) or the like in a car exhaust gas, or a gas separation membrane for selectively separating only p-xylene from a xylene isomer. Moreover, Deca-Dodecasil 3R (DDR) type zeolite is zeolite provided with pores of about 0.44×0.36 nm by oxygen eight-membered rings among crystals, and is utilized in a use application such as a gas separation membrane for selectively separating/removing only carbon dioxide from a natural gas or a biogas to improve purity of methane which is useful as a fuel.
Moreover, for the purpose of removing NOx or the like contained in an exhaust gas discharged from an engine for a car, an engine for a construction machine, an industrial stationary engine, a burning apparatus or the like or adsorbing hydrocarbons or the like contained in the exhaust gas, as a ceramic carrier (a honeycomb structure) made of cordierite or the like and having a honeycomb shape, there is used a catalyst article onto which zeolite subjected to an ion exchange treatment is loaded.
When zeolite is loaded onto the above ceramic carrier made of cordierite or the like, cordierite or the like does not exert a function of removing NOR, a function of adsorbing hydrocarbons or the like. Therefore, when cordierite or the like is present, a pressure loss during passing of the exhaust gas increases.
To solve this problem, there is suggested a method of forming and firing a forming raw material containing zeolite subjected to an ion exchange treatment between cations of zeolite and metal ions, to form a honeycomb structure itself (e.g., see Patent Documents 4 to 6).    [Patent Document 1] JP-A-2007-296521    [Patent Document 2] Japanese Patent No. 3272446    [Patent Document 3] JP-A-2009-000657    [Patent Document 4] JP-A-2008-169104    [Patent Document 5] JP-A-2007-296514    [Patent Document 6] WO2009/141878A1